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Chapter 20
Retrofit procedures of bridge networks against seismic
actions in Italy
A. Pipinato
Department of Civil, Architectural and Environmental Engineering, University of Padova, Italy
ABSTRACT: Existing bridges represent a relevant category of the international cultural
heritage, being the evidence of the modern industrial technology. Many of these structures
require particular rehabilitation due to design defects, basic elements deterioration, variation
of use or intensity change of the imposed loads. With regard to Italy, the historical heritage
is rich of significant structures, which played an essential role in the growth of the industrial
civilization: the most part of this heritage is represented by bridges, and a large part of the
Italian bridges has more than one hundred years. In this paper, a comprehensive overview
on practical issues on the assessment of bridge networks are presented in order to evaluate
the structural integrity of historical and deteriorated bridges, incorporating code aspects,
analytical, mechanical and structural topics.
1 INTRODUCTION
The risk associated to the seismic vulnerability of bridges and infrastructure in general is a
relevant issue to guarantee standard safety and security of citizens in everyday life and more-
over in the case of disaster. In Italy, tragic events have kicked the nation also recently (Aquila
2009 and Emilia 2012), and in the past—in the second half of the 20th century (Friuli 1976
and Irpinia 1980)—even if the transportation infrastructure has not suffered significantly. In
the Apennine mountains crossing of the A16 highway the bridges did undergo some damage,
mainly due to the inadequacy of the bearing devices, but this was promptly remedied by the
owner through the systematic adoption of the seismic isolation. The delay in the apprecia-
tion of the risk is not exclusive to Italy, but also in US, the Federal Highway Administration
(FHWA) published a first document titled “Retrofitting guidelines for Highway Bridges”
some years after (FHWA-ATC 1983) the San Fernando (1971) earthquake. Still, in 1989,
despite of the large retrofit program developed, the Loma Prieta earthquake exposed sub-
stantial deficiencies in bridges in California (Pinto et al., 2011). A relevant number of bridges
and viaducts of medium and large span are present in the national infrastructural system,
Figures 1 and 2. The situation as briefly outlined above is sufficient to understand that the
state of the art on seismic assessment and retrofit of bridges still needs to be advanced in sev-
eral areas. The areas considered to be of priority interest were assessment methods, retrofit
criteria and intervention techniques. Although, a relevant amount of work on existing bridge
network has been performed in the past, a comprehensive overview of recent studies should
help in the identification of the state of knowledge of the matter.
2 SEISMIC ACTIVITY IN ITALY
In the last two thousand years, Italy has been hit by over thousands of medium to strong
earthquakes measuring more than grade V on the Mercalli scale, and by hundreds events of
an intensity equal to or higher than grade VIII on the Mercalli scale. Earthquakes with 1,000
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216 Seismic analysis & design
Figure 1. Aglio Viaduct, Milano-Roma-Napoli Highway.
Figure 2. Italia Viaduct, Salerno-RC Highway.
or more deaths since 1900 (USGS 2013) have been reported in Table 1, while selected earth-
quakes of historic interest in Italy (USGS, 2013) have been reported in Table 2: as could be
inferred from the analysis of available data, in the twentieth century alone, 7 earthquakes had
a magnitude of 6.5 or more (grade X and XI on the Mercalli scale). Disastrous earthquakes
like the long seismic period in 1783 in Calabria (which peaked at grade XI on the Mer-
calli scale), have deeply scarred the land and left recognizable signs of recovery and recon-
struction (Protezione Civile 2013). In the last forty years, the economic damage caused by
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